Abstract

Late Ordovician fossils, including the distinctive Hirnantia brachiopod Fauna, have been found in Lower Palaeozoic successions in Istanbul and Bolu (Yığılca), western Pontides, NW Turkey. The Middle Ordovician (Sandbian) faunas belong to the cooler-water Mediterranean Province, and they are followed by Katian brachiopods including Sulevorthis, Nicolella, Hesperorthis, Glyptorthis, Saukrodictya and Kullervo and ostracods such as Piretella, Eochilina and Klimphores, which represent deposition in warmer waters; however, the Mediterranean Province usually cooler-water brachiopods Drabovia and Leptestiina also occur. The Pendik Formation includes thin bryozoan-rich limestones which probably represent the Boda Global Warming Event. The overlying turbidites contain a Hirnantia Fauna, developed within a brachiopod–diplograptid association. Above them there are characteristic Llandovery (Rhuddanian–Aeronian) brachiopods, such as Leangella, Eoplectodonta, Stricklandia and Hindella with the corals Halysites, Paleofavosites and Streptelasma. In the Bolu area, Katian brachiopods such as Mcewanella, Dalmanella, Glyptorthis, Christiania, Oligorhynchia, Nicolella, Howellites and Drabovinella also occur, but there the overlying Hirnantia Fauna is developed within a HirnantiaMucronaspis association. The fauna and sediments indicate that the western Pontides were not very cold during the latest Ordovician. Despite Turkey being placed in higher latitudes by previous authors, it seems more probable that the Pontides were at somewhat lower palaeolatitudes, perhaps at about 40°S in those times; however, the precise palaeogeographical position of the terrane remains uncertain: there are no Hirnantian glaciogenic rocks there, such as are found in the Taurides of southern Turkey.

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